1. Field of the Invention
The present invention is related with a reproducing apparatus in a case of reproducing, by using one reproducing apparatus, information from a plurality of types of optical record mediums, such as optical disks of various types and the like, to which the information is recorded by a phase pit and the like or a magnetic way, and more particularly, it is related with a judging method and apparatus for judging the type of the optical record medium to be reproduced. It is further related with, in an optical pickup for irradiating a light beam as an information reproducing light to the plurality of types of optical record mediums and reproducing the above mentioned information by use of the reflection light, a focus servo controlling method and apparatus for carrying out a focus servo control in order to beam-condense (focus) the light beam which has an optimal size at a reproducing position of the optical record medium.
2. Description of the Related Art
There is a so-called CD/LD compatible reproducing apparatus which can reproduce a CD (Compact Disk) and a LD (Laser Disk) with one reproducing unit. In this CD/LD compatible reproducing apparatus, a distance from a record medium surface to an information record surface (namely, a thickness of a protecting layer) is common in the CD and the LD (e.g. 1.2 mm in common). Thus, it is possible to reproduce both of these optical disks by using an optical pickup in which a light beam is condensed to one focal point.
In this CD/LD compatible reproducing apparatus, as a rising operation prior to reproducing the record information, a focus servo control is needed for carrying out an optimal focus servo control corresponding to the type of the optical disk to be reproduced. However, in this case, for example, in order to use a conventionally general astigmatism method to thereby carry out the focus servo control, prior to carrying out the focus servo control, it is necessary to do a so-called "focus search action" for setting a standard position when carrying out the appropriate focus servo control. This focus search action moves an optical pickup in a direction perpendicular to the optical disk by a predetermined length to thereby detect an optimal focus position on the basis of a focus error signal (S-shaped signal) outputted at that time. In the above mentioned CD/LD compatible reproducing apparatus, since distances from surfaces of the optical disks to information record surfaces are equal to each other in the CD and the LD, a common action is carried out in both cases in doing the focus search action. Further, in this focus search action, in order to compensate an output power change due to the variation of a reflectivity of the optical disk, the contamination associated with aging of the optical pickup and the like, or a change in a focus servo gain due to the variation of a sensitivity of an optical detector during an optical pickup action and the like, a process is carried out which detects a peak value of the above mentioned focus error signal and re-sets the servo gain corresponding to the peak value.
In the above mentioned CD/LD compatible reproducing apparatus, in a case of judging whether the optical disk mounted in the reproducing apparatus is the CD or the LD, it is judged whether or not the focus servo is locked by moving the optical disk into an area located outside the CD and inside the LD and rotating the optical disk by utilizing a diameter difference between the CD and the LD. Namely, if it is locked, the optical disk is judged as the LD. If it is not locked, the optical disk is judged as the CD.
On the other hand, a DVD (Digital Video Disk) is being developed which greatly improves a memory capacity as compared with a conventional CD and is a high density record medium to which one movie or the like can be recorded. Especially, a CD/DVD compatible reproducing apparatus is being developed which can reproduce both the DVD and the CD.
When comparing a configuration of the CD with that of the DVD, from the viewpoint of a high density request, the thickness of the protecting layer of the DVD is set to a thickness (0.6 mm) approximately half of that of the protecting layer of the CD. Thus, if trying to reproduce both of these optical disks by using the optical pickup having one focal point, for example, if trying to condense a light beam so as to be optimal for the DVD, since the protecting layer of the CD through which the light beam is passed is thicker than that of the DVD, aberration such as spherical aberration and the like is generated in the light beam. This results in a problem that the light beam can not be optimally condensed with respect to the CD.
In order to solve this problem, one method may be considered in which an aberration correcting element is inserted into an optical path of the light beam, depending on the type of the optical disk to be reproduced. However, this method will require a mechanical device which puts and retracts the aberration correcting element into and from the optical path on the basis of the type of the optical disk to be reproduced. Thus, this method is not suited for miniaturization of the optical pickup.
A bifocal lens is developed through which it is possible to irradiate two light beams focused on different positions on one straight line. This bifocal lens is explained with reference to FIGS.6A and 6B.
As shown in FIG. 6A, the bifocal lens comprises a diffraction grating H and an objective lens R arranged on one optical path. A light beam L made into a parallel light by a collimator lens C is divided into three beams of a 0 order light, a +1 order light and a-1 order light by the diffraction grating H. By using a difference between optical path lengths of the 0 order light and the +1 order light among them, the 0 order light and the +1 order light are made focused on different positions on one straight line. More actually, this bifocal lens is adapted such that the +1 order light is focused on a position further from the objective lens R than the 0 order light, and that the 0 order light is optimally beam-condensed on the information record surface of the DVD (e.g. 0.6 mm from the disk surface), and also as shown in FIG. 6B, the +1 order light is optimally beam-condensed on the information record surface of the CD (e.g. 1.2 mm from the disk surface).
If using this bifocal lens, it is possible to use one optical pickup to thereby reproduce both of the CD and the DVD.
Even in a case of using the above mentioned bifocal lens to thereby reproduce information, similarly to the conventional CD/LD compatible reproducing apparatus, the focus search action is required.
From the viewpoint of a high density request, the DVD is superior in linear velocity of record information to the CD. Thus, the focus servo gain and a focus servo frequency band in the focus search action are different between the CD and the DVD. For the focus servo frequency band, more actually, it is necessary that the DVD is widely set on a higher frequency side than the CD.
If trying to apply the conventional focus search action to such a CD/DVD compatible reproducing apparatus, it is necessary to verify two different focus servo gains and focus servo frequency bands and set the focus servo gain and the focus servo frequency band which are adapted to the mounted optical disk. This results in a problem of requiring an unnecessary time for the focus servo action.
Even when judging the optical disk mounted in the CD/DVD compatible reproducing apparatus, since a radius of the CD is equal to that of the DVD, there is a problem that a conventional disk judging method can not be used. In combination with this problem and the above mentioned problem in setting the focus servo gain and the focus servo frequency band, judging of the optical disk and setting of the focus servo gain and the focus servo frequency band are separately carried out, so that it is impossible to carry out a rapid rising operation at the beginning of reproducing the record information, which is another problem.